6 Classification of Soils. 



20. The state of division of the soil, as to whether coarse or fine, 

 has also an important influence, especially with reference to its per- 

 meability by water, its drainage, and the like. Upon these proper- 

 ties, and the organic materials, in connection with the local climate, 

 the fertility of a given soil may be said to depend. 



21. It matters not what the chemical or physical properties of the 

 soil may be, it will remain unproductive unless there be seasonable 

 and sufficient rains, or their equivalent supplied by irrigation, and 

 unless the conditions of temperature be consistent with vegetable 

 growth. 



22. Although soils present infinite variety in their constituent 

 parts, they may be classed under four principal divisions, viz.: si- 

 liceous, calcareous, argillaceous, and alkaline. 



23. In siliceous soils, the principal constituent is gravel or sand, 

 composed of silex or quartz, more or less finely divided, and nearly 

 or quite destitute of the power of absorbing of retaining water, un- 

 less underlaid by a retentive sub-soil, or unless it is but moderately 

 above the level of a standing water, from which, by capillary attrac- 

 tion, its moisture may be drawn. 



24. In calcareous soils, the carbonate of lime is found, either from 

 the decomposition of limestones, or from marls of more recent or- 

 ganic origin. Such soils have the property of absorbing and retain- 

 ing moisture in a high degree, but, although saturated they do not 

 become impenetrable to the air, and when turned up aud exposed 

 to its action they fall to dust, and this the more readily when as- 

 sisted by frost. They will effervesce when thrown into acids, and 

 this affords a convenient, but not absolute test. 



25. In argillaceous soils, the silicate of alumina, in the form of clay, 

 forms the principal ingredient. These soils have a strong affinity 

 for water, and hold it with great tenacity ; yet, when exposed to 

 solar heat, they crack into deep fissures in times of drouth. The 

 water that falls upon clay soils does not penetrate, and they often af- 

 ford much resistance to the roots of plants. 



26. In alkaline soils, the soluble salts of soda are in excess. Where 

 these soils occur, there is a noted deficiency in the rain fall, and a 

 marked sterility from this cause, for the excess of alkali appears 

 principally due to the want of moisture for dissolving it out and car- 

 rying it away. When such soils are irrigated, they become fertile, 

 and improve as the excess of alkali is reduced. A lime-like deposit 



